Liquid crystal display and thin film transistor array panel therefor

ABSTRACT

A liquid crystal display (LCD) is provided, which includes: first and second gate lines, a data line intersecting the gate lines, first to fourth drain electrodes located near the intersections between the first and second gate lines and the data line, and a coupling electrode. First to fourth pixel electrodes respectively connected to the first to fourth drain electrodes are also provided, and the first pixel electrode is connected to the coupling electrode while the fourth pixel electrode overlaps the coupling electrode. The LCD further includes a common electrode opposite the pixel electrodes, a liquid crystal layer interposed between the pixel electrodes and the common electrode, and a domain partitioning member formed on at least one of the pixel electrode and the common electrode. Two long edges of the domains are angled with respect to the first and the second gate lines or the data line substantially by about 45°.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/820,687, filed Jun. 22, 2010, which is a continuation of U.S. patentapplication Ser. No. 11/845,438, filed Aug. 27, 2007, which is acontinuation of U.S. patent application Ser. No. 11/043,157, filed Jan.27, 2005, issued as U.S. Pat. No. 7,280,177 on Oct. 9, 2007, which is acontinuation of U.S. Ser. No. 10/602,710, filed on Jun. 25, 2003, issuedas U.S. Pat. No. 6,850,302 on Feb. 1, 2005, which claims priority toKorean Patent Application No. 2002-0036979, filed Jun. 28, 2002. Thedisclosures of the above-cited applications are incorporated byreference herein in their entireties.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a liquid crystal display, and inparticular, to a panel for the liquid crystal display.

(b) Description of Related Art

Generally, a liquid crystal display (LCD) includes a liquid crystal (LC)panel assembly including two panels provided with two kinds of fieldgenerating electrodes such as pixel electrodes and a common electrodeand a LC layer with dielectric anisotropy interposed therebetween. Thevariation of the voltage difference between the field generatingelectrodes, i.e., the variation in the strength of an electric fieldgenerated by the electrodes changes the transmittance of the lightpassing through the LCD, and thus desired images are obtained bycontrolling the voltage difference between the electrodes.

However, the LCD involves a critical shortcoming of the narrow viewingangle. In order to overcome such a problem, various techniques for widenthe viewing angle have been developed, and among them, a technique offorming cutouts or protrusions at the pixel electrodes and the commonelectrode while aligning the LC molecules vertical to the upper andlower panels is the strongest candidate for the wide viewing angletechnique.

The cutouts provided at the respective pixel electrodes and the commonelectrode generate fringe fields, which control the tilt directions ofthe LC molecules are controlled to thereby widen the viewing angle.

The protrusions provided on the respective pixel electrodes and thecommon electrode deform the electric field, and the tilt directions ofthe LC molecules are controlled due to the deformed electric field tothereby widen the viewing angle.

Alternatively, the cutouts are provided at the pixel electrodes of alower panel while protrusions are provided at the common electrode of anupper panel. Fringe fields generated by the cutouts and the protrusionscontrols the tilt directions of the LC molecules to thereby formmultiple domains.

The multi-domain LCD involves a very excellent contrast-based viewingangle or gray inversion-based viewing angle of up to 80° or more in alldirections. The contrast-based viewing angle is defined as a viewingangle showing the contrast ratio of 1:10, and the gray inversion-basedviewing angle is defined by the limit angle of the inter-gray luminanceinversion. However, the multi-domain LCD shows a lateral gamma curvedistortion that the front gamma curve and the lateral gamma curve do notagree to each other is made to exhibit deteriorated left and rightvisibility even compared with the twisted nematic (TN) mode LCD. Forinstance, the patterned vertically aligned (PVA) mode LCD having cutoutsfor partitioning domains becomes brighter and color-shifts to white asit goes to the lateral sides. In a serious case, the difference betweenthe bright grays is eradicated, and hence, the images becomeconglomerated. However, it becomes a critical matter to improve thevisibility more and more as the LCD has been recently used for themultimedia purpose to display still or moving picture images.

SUMMARY OF THE INVENTION

A liquid crystal display is provided, which includes: a first insulatingsubstrate; first and second signal lines formed on the first insulatingsubstrate; a third signal line formed on the first insulating substrateand crossing the first and the second signal lines; a first thin filmtransistor connected to the first and the third signal lines; a secondthin film transistor connected to the second and the third signal lines;a first pixel electrode connected to the first thin film transistor; asecond pixel electrode connected to the second thin film transistor; asecond insulating substrate facing the first insulating substrate; acommon electrode formed on the second insulating substrate; a liquidcrystal layer interposed between the first and the second insulatingsubstrates and including a first liquid crystal region on the firstpixel electrode and a second liquid crystal region on the second pixelelectrode; and a domain partitioning member formed on at least one ofthe first and the second insulating substrates for partitioning thefirst and the second liquid crystal regions into a plurality of domains,respectively, wherein the domains of each of the first and the secondliquid crystal regions includes a first directional domain and a seconddirectional domain, the average directors of liquid crystal molecules inthe first and the second directional domains are angled with respect tothe first or the second signal line by a predetermined degree of about0-90°, and the first pixel electrode and the second pixel electrode arecapacitively coupled.

It is preferable that the first pixel electrode occupies about 50-80% ofan entire area of the first and the second pixel electrodes, and thesecond thin film transistor is activated after the first thin filmtransistor is activated.

The threshold voltage of the first pixel electrode is preferably lowerthan the threshold voltage of the second pixel electrode by about0.4-1.0V.

The liquid crystal display may further includes a storage electrode lineformed on the first substrate and forming storage capacitors along withthe first and the second pixel electrodes.

The average director of the liquid crystal molecules in the first andthe second directional domains are preferably angled with respect to thefirst or the second signal line by about 45°.

Preferably, the liquid crystal display further includes a firstpolarizer placed on an outer surface of the first substrate and having apolarizing axis parallel to the first or the second signal line, and asecond polarizer placed on an outer surface of the second substrate andhaving a polarizing axis crossing the polarizing axis of the firstpolarizing plate.

A thin film transistor array panel is provided, which includes: aninsulating substrate; first and second gate lines formed on thesubstrate; a gate insulating layer formed on the first and the secondgate lines; a semiconductor layer formed on the gate insulating layer; adata line formed at least on the semiconductor layer and intersectingthe gate lines; first and second drain electrodes formed at least on thesemiconductor layer and located near the intersection between the firstgate line and the data line; third and fourth drain electrodes formed atleast on the semiconductor layer and located near the intersectionbetween the second gate line and the data line; a coupling electrodeformed on the gate insulating layer; a passivation layer formed on thedata line, the first to the fourth drain electrodes, and the couplingelectrode and having a plurality of contact holes exposing the first tothe fourth drain electrodes and the coupling electrode; a first pixelelectrode formed on the passivation layer and connected to the firstdrain electrode and the coupling electrode; a second pixel electrodeformed on the passivation layer and connected to the second drainelectrode; a third pixel electrode formed on the passivation layer andconnected to the third drain electrode; and a fourth pixel electrodeformed on the passivation layer and connected to the fourth drainelectrode and partially overlapping the coupling electrode, wherein atleast one of the first and the fourth pixel electrodes has an obliquecutout.

A liquid crystal display is provided, which includes: a first insulatingsubstrate; first and second gate lines formed on the first substrate; agate insulating layer formed on the first and the second gate lines; asemiconductor layer formed on the gate insulating layer; a data lineformed at least on the semiconductor layer and intersecting the gatelines; first and second drain electrodes formed at least on thesemiconductor layer and located near the intersection between the firstgate line and the data line; third and fourth drain electrodes formed atleast on the semiconductor layer and located near the intersectionbetween the second gate line and the data line; a coupling electrodeformed on the gate insulating layer; a passivation layer formed on thedata line, the first to the fourth drain electrodes, and the couplingelectrode and having a plurality of contact holes exposing the first tothe fourth drain electrodes and the coupling electrode; a first pixelelectrode formed on the passivation layer and connected to the firstdrain electrode and the coupling electrode; a second pixel electrodeformed on the passivation layer and connected to the second drainelectrode; a third pixel electrode formed on the passivation layer andconnected to the third drain electrode; a fourth pixel electrode formedon the passivation layer and connected to the fourth drain electrode andpartially overlapping the coupling electrode; a second insulatingsubstrate facing the first insulating substrate; a common electrodeformed on the second insulating substrate; a liquid crystal layerinterposed between the first and the second insulating substrates; and adomain partitioning member formed on at least one of the first and thesecond insulating substrates and partitioning the liquid crystal layerinto a plurality of domains, wherein two long edges of the domains areangled with respect to the gate line or the data line substantially byabout 45°.

Preferably, the first pixel electrode occupies about 50-80% of an entirearea of the first and the fourth pixel electrodes and the fourth pixelelectrode is supplied with a voltage after the first pixel electrode issupplied with a voltage.

The threshold voltage of the first pixel electrode is preferably lowerthan the threshold voltage of the fourth pixel electrode by about0.4-1.0V.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the present invention will become moreapparent by describing preferred embodiments thereof in detail withreference to the accompanying drawings in which:

FIG. 1 is a circuit diagram of an LCD according to an embodiment of thepresent invention;

FIG. 2 is a layout view of an LCD according to an embodiment of thepresent invention;

FIG. 3A is a sectional view of the LC panel assembly shown in FIG. 2taken along the line IIIB-IIIB′;

FIG. 3B is a sectional view of a TFT array panel shown in FIG. 3A, whichis a portion of the LC panel assembly shown in FIG. 3A except for acolor filter array panel and polarization films;

FIG. 3C is a sectional view of a TFT array panel shown in FIG. 2 takenalong the line IIIC-IIIC′;

FIG. 4 is a graph illustrating the distortion in the visibility as afunction of the voltage shift and the domain ratio;

FIG. 5 is a graph illustrating gamma curves for a front view and alateral view of a conventional patterned-vertically-aligned (PVA) LCD;

FIG. 6 is a graph illustrating gamma curves for a front view and alateral view of an LCD according to an embodiment of the presentinvention;

FIG. 7 illustrates measured gamma curves of a conventional PVA mode LCD;and

FIG. 8 illustrates measured gamma curves of an LCD according to anembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein.

In the drawings, the thickness of layers, films and regions areexaggerated for clarity. Like numerals refer to like elementsthroughout. It will be understood that when an element such as a layer,film, region or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. In contrast, when an element is referred to as being“directly on” another element, there are no intervening elementspresent.

Now, LCDs according to embodiments of this invention will be describedin detail with reference to the accompanying drawings.

FIG. 1 is an equivalent circuit diagram of a pixel of an LCD accordingto an embodiment of the present invention.

Referring to FIG. 1, an LCD according to an embodiment includes aplurality of display signal lines G_(i), D_(j) and 131 and a pluralityof pixels connected thereto and arranged substantially in a matrix.

The display signal lines G_(i) and D_(j) include a plurality of gatelines G_(i) transmitting gate signals (called scanning signals) and aplurality of data lines D_(j) transmitting data signals. The gate linesG_(i) extend substantially in a row direction and are substantiallyparallel to each other, and the data lines D_(j) extend substantially ina column direction and are substantially parallel to each other.

The display signal lines 131 further includes a plurality of storageelectrode lines 131 located between the gate lines G_(i) and between thepixels and supplied with a common voltage Vcom.

Each pixel P_(ij) (i=1, 2, . . . , n and j=1, 2, . . . , m) includes apair of subpixels P_(i,j) ¹ and P_(i,j) ², and each subpixel P_(i,j) ¹or P_(i,j) ² includes a switching element Q1 or Q2 connected to a pairof one of the gate lines G_(i) and one of the data lines D_(j), and anLC capacitor C_(LC1) or C_(LC2) and a storage capacitor C_(ST1) orC_(ST2) that are connected to the switching element Q1 or Q2.

Two adjacent pixels in the column direction are capacitively coupled bya coupling capacitor Cpp. For example, an upper subpixel P_(i,j) ¹ of apixel P_(ij) is capacitively coupled with a lower subpixel P_(i,j) ² ofan upper pixel P_(i−1j), and a lower subpixel P_(i,j) ² of a pixelP_(ij) is capacitively coupled with an upper subpixel P_(i+1,j) ¹ of alower pixel P_(i+1,j).

The switching element Q1 or Q2 has three terminals: a control terminalconnected to one of the gate lines G₁-G_(n); an input terminal connectedto one of the data lines D₀-D_(m); and an output terminal connected tothe LC capacitor C_(LC1) or C_(LC2), the storage capacitor C_(ST1) orC_(ST2), and the coupling capacitor Cpp.

The LC capacitor C_(LC1) or C_(LC2) is connected between the switchingelement Q1 or Q2 and a common voltage Vcom. The storage capacitorC_(ST1) or C_(ST2) is connected between the switching element Q1 or Q2and the storage electrode line 131.

Now, an LC panel assembly for an LCD according to an embodiment of thepresent invention is described in detail with reference to FIGS. 2 to3C.

FIG. 2 is a layout view of an LC panel assembly according to anembodiment of the present invention, FIG. 3A is a sectional view of theLC panel assembly shown in FIG. 2 taken along the line IIIB-IIIB′, andFIG. 3B is a sectional view of a TFT array panel shown in FIG. 3A, whichis a portion of the LC panel assembly shown in FIG. 3A except for acolor filter array panel and polarization films. FIG. 3C is a sectionalview of a TFT array panel shown in FIG. 2 taken along the lineIIIC-IIIC′.

Referring to FIG. 3A, an LC panel assembly according to this embodimentincludes a TFT array panel 100, a color filter array panel 200 facingthe TFT array panel 100, and an LC layer 3 interposed therebetween.

Referring to FIGS. 2 to 3C, the TFT array panel 100 includes a pluralityof gate lines 121 and a plurality of storage electrode lines 131 formedon an insulating substrate 110 preferable made of transparent glass.Each gate line 121 extends substantially in a row direction and includesa plurality of gate electrodes 124. The storage electrode lines 131extend substantially in the row direction and are partially curved.

A gate insulating layer 140 is formed on the gate lines 121 and thestorage electrode lines 131, and a plurality of semiconductor islands154 is formed on the gate insulating layer 140 opposite the gateelectrodes 124. Each semiconductor island 154 is preferably made ofamorphous silicon (“a-Si”) and forms a channel of a TFT. A plurality ofohmic contacts 163, 165 a and 165 b preferably made of a-Si heavilydoped with N type impurity such as phosphorous (P) are formed on thesemiconductor islands 154.

A plurality of data lines 171, a plurality of pairs of drain electrodes175 a and 175 b, and a plurality of coupling electrodes 177 are formedon the ohmic contacts 163, 165 a and 165 b and the gate insulating layer140.

Each data line 171 extends substantially in a column direction andincludes a plurality of source electrodes 173, and each source electrode173 is located opposite a pair of drain electrodes 175 a and 175 bseparated therefrom with respect to the gate electrode 124.

Each pair of drain electrodes 175 a and 175 b extends oppositedirections with respect to the gate line 124.

Each coupling electrode 177 extends in the column direction across thestorage electrode line 131.

The portions of the semiconductor islands 154 located between the sourceelectrode 173 and the drain electrodes 175 a and 175 b are exposed, andthe ohmic contacts 163, 165 a and 165 b are disposed only between thesemiconductor islands 154 and the data lines 171 and the drainelectrodes 175 a and 175 b.

A passivation layer 180 is formed on the data lines 171, the drainelectrodes 175 a and 175 b, and the coupling electrodes 177. Thepassivation layer 180 has a plurality of contact holes 185 a and 185 bexposing end portions of the drain electrodes 175 a and 175 b and aplurality of contact holes 187 exposing end portions of the couplingelectrodes 177. The passivation layer 180 further has a plurality ofcontact holes 182 exposing end portions 179 of the data lines 171, andthe passivation layer 180 and the gate insulating layer 140 have aplurality of contact holes 181 exposing end portions 129 of the gatelines 121.

A plurality of pairs of pixel electrodes 190 a and 190 b and a pluralityof contact assistants 81 and 92 are formed on the passivation layer 180.The pixel electrodes 190 a and 190 b and the contact assistants 81 and92 are preferably made of a transparent conductive material such asindium-tin-oxide (ITO) and indium-zinc-oxide (IZO) or a reflectivematerial.

Each pair of pixel electrodes 190 a and 190 b includes a lower pixelelectrode 190 a and an upper pixel electrode 190 b connected to thedrain electrodes 175 a and 175 b through the contact holes 185 a and 185b, respectively. The upper electrode 190 b is connected to the couplingelectrode 177 through the contact hole 187 and the lower electrode 190 aoverlaps the coupling electrode 177 such that the lower pixel electrode190 a of an upper pixel and the upper pixel electrode 190 b of a lowerpixel are capacitively coupled. In addition, the lower pixel electrode190 a of an upper pixel and the upper pixel electrode 190 b of a lowerpixel are located opposite across the storage electrodes line 131 andoverlap the storage electrode line 131 to form a plurality of storagecapacitors. The edges of the pixel electrodes 190 a and 190 b oppositeacross the storage electrode line 131 are curved to form V shapes, andthe V-shaped edge of the pixel electrode 190 a is convex, while that ofthe pixel electrode 190 b is concave.

Each lower pixel electrode 190 a has upper, lower and central linearcutouts 91-93. The central cutout 93 is located at the middle portion inthe column direction and enters into the pixel electrode 190 a from theleft to the right, thereby partitioning the pixel electrode 190 a intoupper and lower partitions. The upper and the lower cutouts 91 and 92obliquely extend in the upper and the lower partitions, respectively,and are located symmetrically with respect to the central cutout 93.

The contact assistants 81 and 82 are connected to the exposed endportions 129 and 179 of the gate lines 121 and the data lines 171through the contact holes 181 and 182, respectively, and provided forprotecting the exposed end portions 129 and 179 but is optional.

An alignment layer 11 is coated on the entire surface of the TFT arraypanel 100 except for the contact assistants 81 and 82.

One gate electrode 124, one source electrode 173, and a pair of drainelectrodes 175 a and 175 b along with one semiconductor island 154 forma pair of TFTs respectively connected to the pixel electrodes 190 a and190 b.

Referring to FIGS. 2 and 3B, the color filter array panel 200 includes ablack matrix 220 formed on an insulating substrate 210 preferably madeof transparent glass. The black matrix 220 defines a plurality ofwindows where a plurality of red, green and blue color filters 230 areformed. An overcoat is formed on the color filters and a commonelectrode 270 is formed thereon. The common electrode 270 is preferablymade of a transparent conductive material such as ITO and IZO, and has aplurality of sets of four linear cutouts 271-274. Three 271-273 of thecutouts 271-274 overlap the lower pixel electrode 190 a to partition thepixel electrode 190 a along with the cutouts 91-93 into a plurality ofsubareas. The cutout 274 having a V shape overlap the upper electrode190 b to bisect the upper pixel electrode 190 b into two subareas. Analignment layer 21 is coated on the entire surface of the color filterarray panel 200.

Each subarea defined by the cutouts 91-93 and 271-273 has substantiallya shape of a tetragon having two major edges making an angle of about 45degrees with the gate lines 121 and the data lines 171. The subareasdefined by edges of the upper pixel electrode 190 b and the cutout 274have V shapes, which are combinations of two tetragons.

A pair of polarizers 12 and 22 are attached to outer surfaces of thepanels 100 and 200, respectively. The polarization, axes of thepolarizers 12 and 22 are crossed and substantially parallel to the gatelines 121 or the data lines 171.

The molecules of the LC layer 3 are aligned such that their major axesare substantially perpendicular to the surfaces of the panels 100 and200 in absence of electric field.

Referring back to FIG. 1, the difference between the data voltage andthe common voltage Vcom applied to a pixel is expressed as a chargedvoltage of the LC capacitor C_(LC1) or C_(LC2), i.e., a pixel voltage.The LC molecules have orientations depending on the magnitude of thepixel voltage and the orientations determine the polarization of lightpassing through the LC capacitor C_(LC1) or C_(LC2). The polarizers 11and 21 convert the light polarization into the light transmittance.

In the meantime, it is assumed that the difference between a datavoltage for a pixel Pup and the common voltage Vcom is d_(up), and pixelvoltages charged in LC capacitors C_(LC1) and C_(LC2) of the upper andthe lower subpixels P_(up) ¹ and P_(up) ² of the pixel Pup are V(P_(up)¹) and V(P_(up) ²), respectively. In addition, let us assume that thelower subpixel P_(up) ² of the pixel Pup and the upper subpixel P_(down)¹ of the pixel Pdown are coupled with a coupling capacitor Cpp, and thedifference between the data voltage for the pixel Pdown and the commonvoltage Vcom is d_(down). Furthermore, after the pixel Pup is suppliedwith the data voltage, the pixel Pdown is supplied with the datavoltage. Then, the following relations are satisfied:

$\begin{matrix}{{{V\left( P_{up}^{1} \right)} = d_{up}};{and}} & (1) \\{{V\left( P_{up}^{2} \right)} = {d_{up} + {\frac{Cpp}{C_{{LC}\; 2} + C_{{ST}\; 2} + {Cpp}} \cdot {\left( {d_{down} - d_{down}^{\prime}} \right).}}}} & (2)\end{matrix}$

In Equations 1 and 2, C_(LC2) and C_(ST2) are the capacitances of the LCcapacitor and the storage capacitor of the lower subpixel P_(up) ², Cppis the capacitance of the coupling capacitor, and d′_(down) is thedifference between the data voltage applied to subpixel P_(down) ¹ in aprevious frame and the common voltage Vcom. For descriptive convenience,the wire resistance and the signal delay of the data lines D_(j) areignored.

In Equation 2, if d_(down) and d′_(down) have opposite polarity sinced_(up) and d_(down) have the same polarity, the pixel Pdown displays thesame gray as the pixel Pup, and the displayed images are still images,d_(up)=d_(down)=−d_(down) and thus Equation 2 becomes:

$\begin{matrix}{{{V\left( P_{up}^{2} \right)} = {{d_{up} + \frac{2d_{up}{Cpp}}{C_{{LC}\; 2} + C_{{ST}\; 2} + {Cpp}}} = {{\frac{C_{{LC}\; 2} + C_{{ST}\; 2} + {3{Cpp}}}{C_{{LC}\; 2} + C_{{ST}\; 2} + {Cpp}}d_{up}} = {T_{1}d_{up}}}}},\mspace{79mu} {{{where}\mspace{14mu} T\; 1} = {\frac{C_{{LC}\; 2} + C_{{ST}\; 2} + {Cpp}}{C_{{LC}\; 2} + C_{{ST}\; 2} + {Cpp}} > 1.}}} & (3)\end{matrix}$

On the contrary, if d_(up) and d_(down) have opposite polarities, thepixel Pdown displays the same gray as the pixel Pup, and the displayedimages are still images, Equation 2 becomes:

$\begin{matrix}{{{V\left( P_{up}^{2} \right)} = {{d_{up} - \frac{2d_{up}{Cpp}}{C_{{LC}\; 2} + C_{{ST}\; 2} + {Cpp}}} = {{\frac{C_{{LC}\; 2} + C_{{ST}\; 2} - {Cpp}}{C_{{LC}\; 2} + C_{{ST}\; 2} + {Cpp}}d_{up}} = {T_{2}d_{up}}}}},\mspace{79mu} {{{where}\mspace{14mu} T\; 2} = {\frac{C_{{LC}\; 2} + C_{{ST}\; 2} - {Cpp}}{C_{{LC}\; 2} + C_{{ST}\; 2} + {Cpp}} < 1.}}} & (4)\end{matrix}$

According to Equations 3 and 4, if a lower subpixel P_(up) ² of a pixelPup is capacitively coupled with a upper subpixel P_(down) ¹ of a pixelPdown, the lower subpixel P_(up) ² of the pixel Pup is charged with avoltage higher than that charged in the upper subpixel P_(up) ¹ of thepixel Pup when the polarity of the data voltages applied to the twosubpixels P_(up) ² and P_(down) ¹ is the same, and vice versa when thepolarity is opposite.

This pixel structure that a pixel includes two switching elements andtwo LC capacitors and adjacent pixels are capacitively coupled by acoupling capacitor prevents gray inversion at a bottom view and improvesvisibility at all directions.

FIG. 4 is a graph illustrating the distortion in the visibility asfunction of the voltage shift and the areal ratio of the pixelelectrodes.

The vertical axis shown in FIG. 4 indicates the value of quantifying thedistortion in the visibility, and the horizontal axis indicates theareal ratio between lower and upper pixel electrodes 190 a and 190 b forthe voltage shifts 0, 0.4V and 0.6V.

The visibility distortion in a range of 0.1-0.2 means that thevisibility is exceptionally excellent, which is equal to the level ofthe cathode ray tube (CRT), and the visibility distortion in a range of0.2-0.25 means that the visibility is very excellent. The visibilitydistortion in a range of 0.25-0.3 means that the visibility isexcellent, and the visibility distortion in a range of 0.3-0.35 meansthat the visibility is good. However, the visibility distortion lessthan about 0.35 means that the visibility is bad, which results in thepoor display quality.

It is known from FIG. 4 that an excellent visibility is obtained whenthe areal ratio of the lower pixel electrode to the upper pixelelectrode is in a range of 50:50-80:20, and when the voltage shift is ina range of 0.4-1.0V close to a threshold voltage Vth. That is, the lowerpixel electrode is preferably designed to be larger than the upper pixelelectrode. However, when the lower pixel electrode is equal to or largerthan 80%, various problems such as a flicker phenomenon may be made dueto the kick-back voltage or other factors. Furthermore, when thethreshold voltage Vth of the lower pixel electrode is lower than thethreshold voltage Vth of the upper pixel electrode by 0.4-1.0V, thevisibility is improved. The voltage difference between the lower and theupper pixel electrodes for the higher grays may be greater.

Then, the reason why the visibility is improved with the LCD accordingto the present invention will be now described with reference to FIGS. 5and 6.

FIG. 5 is a graph illustrating gamma curves C1 and C2 respectively for afront view and a lateral view of a conventionalpatterned-vertically-aligned (PVA) LCD, and FIG. 6 is a graphillustrating gamma curves C3 and C4 respectively for a front view and alateral view of an LCD according to an embodiment of the presentinvention.

As shown in FIG. 5, the lateral gamma curve C2 of a conventional PVA LCDhaving one pixel electrode for a pixel is largely deformed upwardcompared with the front gamma curve C1.

However, according to an embodiment of the present invention, when thedata voltage is established such that the pixel voltage applied to thelower subpixel is lower than the usual data voltage, the voltage of thelower subpixel may be kept to be lower than a threshold voltage Vth forsome lower grays. Accordingly, the lower subpixel is kept to be in ablack state, while the upper subpixel exhibits a transmitting state asindicated by reference character A in FIG. 6. However, since the area ofthe upper pixel electrode is small, the total luminance is small thanthat of a conventional LCD. For the gray equal to or larger than apredetermined value (indicated by reference character B), the voltage ofthe lower subpixel exceeds the threshold voltage Vth, and hence, thelower subpixel also contributes to the total luminance. Therefore, theincrease of the luminance depending on the gray increase is enlarged.Accordingly, as shown in FIG. 6, the distortion in the gamma curvebecomes decreased.

FIG. 7 illustrates measured gamma curves of a conventional PVA mode LCD,and FIG. 8 illustrates measured gamma curves of an LCD according to anembodiment of the present invention.

Comparing the gamma curves illustrated in FIGS. 7 and 8, it can be knownthat the gamma curve distortion for all directions of the LCD accordingto the embodiment of the present invention be smaller than that of theconventional LCD for all directions.

As described above, two pixel electrodes and two TFTs are assigned toone pixel, and the two pixel electrodes of adjacent two pixels arecapacitively coupled, thereby improving the visibility in alldirections. Furthermore, as the domain partitioning is made such thatthe average director of the liquid crystal molecules is angled withrespect to the gate line or the data line by 45°, polarizers havingpolarizing axes parallel to the gate line or the data line can be used.Consequently, the production cost for the polarizing plate can bereduced.

Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

1. A liquid crystal display, comprising: a first substrate comprising: apixel electrode comprising a first subpixel electrode and a secondsubpixel electrode, the first and the second subpixel electrodes beinglocated at a same layer; and a first polarizer having a first polarizingaxis; a second substrate facing the first substrate, and comprising asecond polarizer having a second polarizing axis crossing the firstpolarizing axis; and a liquid crystal layer interposed between the firstsubstrate and the second substrate, wherein the liquid crystal layer oneach of the first subpixel electrode and the second subpixel electrodeis divided into a plurality of domains, at least one of the plurality ofdomains being defined by a direction of liquid crystal molecules when anelectric field is applied, and a value of an electric field on thesecond subpixel electrode is weaker than a value of an electric field onthe first subpixel electrode, and wherein the directions of the liquidcrystal molecules of the domains are angled with respect to the firstand the second polarizing axes in a plan view.
 2. The liquid crystaldisplay of claim 1, further comprising: first signal lines disposed onthe first substrate; a first thin film transistor electrically connectedto one of the first signal lines and the first subpixel electrode,respectively; and a second thin film transistor electrically connectedto the one of the first signal lines and the second subpixel electrode,respectively.
 3. The liquid crystal display of claim 2, furthercomprising second signal lines, each of which is disposed between twoadjacent first signal lines, and overlaps the first subpixel electrodeor the second subpixel electrode.
 4. The liquid crystal display of claim3, wherein the domains of the liquid crystal layer are defined by adomain partitioning member formed on at least one of the first substrateand the second substrate.
 5. The liquid crystal display of claim 4,wherein the liquid crystal layer is divided into at least four domains.6. The liquid crystal display of claim 5, wherein an area of the firstsubpixel electrode is different from an area of the second subpixelelectrode.
 7. The liquid crystal display of claim 2, wherein the domainsof the liquid crystal layer are defined by a domain partitioning memberformed on at least one of the first substrate and the second substrate.8. The liquid crystal display of claim 7, wherein the liquid crystallayer is divided into at least four domains.
 9. The liquid crystaldisplay of claim 8, wherein an area of the first subpixel electrode isdifferent from an area of the second subpixel electrode.
 10. The liquidcrystal display of claim 2, wherein the liquid crystal layer is dividedinto at least four domains.
 11. The liquid crystal display of claim 10,wherein an area of the first subpixel electrode is different from anarea of the second subpixel electrode.
 12. The liquid crystal display ofclaim 2, wherein an area of the first subpixel electrode is differentfrom an area of the second subpixel electrode.
 13. The liquid crystaldisplay of claim 1, further comprising: first signal lines disposed onthe first substrate, one of the first signal lines being electricallyconnected to at least one thin film transistor, the at least one thinfilm transistor being electrically connected to the pixel electrode; andsecond signal lines, each of which is disposed between two adjacentfirst signal lines, and overlaps the first subpixel electrode or thesecond subpixel electrode.
 14. The liquid crystal display of claim 13,wherein the domains of the liquid crystal layer are defined by a domainpartitioning member formed on at least one of the first substrate andthe second substrate.
 15. The liquid crystal display of claim 14,wherein the liquid crystal layer is divided into at least four domains.16. The liquid crystal display of claim 15, wherein an area of the firstsubpixel electrode is different from an area of the second subpixelelectrode.
 17. The liquid crystal display of claim 13, wherein theliquid crystal layer is divided into at least four domains.
 18. Theliquid crystal display of claim 17, wherein an area of the firstsubpixel electrode is different from an area of the second subpixelelectrode.
 19. The liquid crystal display of claim 13, wherein an areaof the first subpixel electrode is different from an area of the secondsubpixel electrode.
 20. The liquid crystal display of claim 1, whereinthe domains of the liquid crystal layer are defined by a domainpartitioning member formed on at least one of the first substrate andthe second substrate.
 21. The liquid crystal display of claim 20,wherein the liquid crystal layer is divided into at least four domains.22. The liquid crystal display of claim 21, wherein an area of the firstsubpixel electrode is different from an area of the second subpixelelectrode.
 23. The liquid crystal display of claim 20, wherein an areaof the first subpixel electrode is different from an area of the secondsubpixel electrode.
 24. The liquid crystal display of claim 1, whereinthe liquid crystal layer is divided into at least four domains.
 25. Theliquid crystal display of claim 24, wherein an area of the firstsubpixel electrode is different from an area of the second subpixelelectrode.
 26. The liquid crystal display of claim 1, wherein an area ofthe first subpixel electrode is different from an area of the secondsubpixel electrode.